Good afternoon security fanatics. Back again today with a brief walk-through of a stored XSS (Cross Site Scripting) that I recently discovered in another wordpress poll plugin. YOP Polls, active on over 20,000 sites, allows users to create interactive and aesthetic polls that are fully customizable and perfect for data collection.

YOP Poll
Use a full option polling solution to get the answers you need. YOP Poll is the perfect, easy to use poll plugin for your WordPress site.

Identifying Reflection

I noticed that there was options when creating a poll to allow "Other" answers. There was also an option to display these other answers on the results screen, which is likely something that a user would enable, in my opinion.

Required Environment for Exploit

I started to play about, testing for different injection types and XSS payloads. To my surprise, the results page reflected the answer back to me as a heading when I stuck it in <h1>tags</h1>. I then opened a new browser without a session and voted to view the results page again. The heading was still there! Therefore, I concluded that I'd discovered some form of stored XSS. I checked if I could use <script> tags too, and sure enough, it worked.

Popping an Alert

Reporting the Vulnerability

I promptly contacted YOP Polls developer and it was fixed within a week with some fantastic contact. The changes made included making use of the esc_html tags before echoing anything back to the user, as seen below.

Exploring the Changes

Proof of Concept

Proof of Concept

Systems Affected

WordPress websites running "YOP Polls" plugin version 6.2.7 (older versions may also be affected).

Remediation

The update has been fixed in version 6.2.8, so it is advised to update to this version if using the plugin.

DISCLOSURE TIMELINE

June 9, 2021 1: Vulnerability identified.
June 9, 2021 2: Informed developer of the vulnerability.
June 10, 2021 1: Vendor requested proof of concept.
June 10, 2021 2: Sent proof of concept and accompanying details.
June 14, 2021 1: Vendor emails to state the vulnerability has been fixed.
June 16, 2021 1: Confirmed fix, vendor happy to disclose the vulnerability.
June 17, 2021 1: Requested CVE Number.